sealing options other than epoxy

This is one of those queries regarding techniques/processes for lightweight building.
I'm currently building a racing craft and a mate of mine is building a hollow timber surfboard. His plans don't call for any use of epoxy to seal internally and he intends to seal the inside surfaces by either painting or using a a penetrating oil such as penetrol.
If an internal surface needs to be sealed against water ingress but structural strength is not an issue, would a penetrating oil be a lightweight (and cheaper) alternative to a coat of expoxy?
Thougts anybody??

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RE: sealing options other than epoxy

Penetrating oils are volatile and very runny. They're meant to aid in the transport and absorption of viscous compounds., then evaporate, not hang around to form a waterproof barrier. Inside a sealed space they will evaporate into the air in the sealed space.

If enough oil is applied, the air will saturate and any remaining oil will wander through the wood fibers. Your friend would have to apply enough oil so that what remains in the wood would displace any water that may get in. But, since the water could only get in through cracks and pinholes, the oil in the air would escape through the same pinholes allowing the oil in the wood to evaporate.

The other problem is stability. As the oil loses its volatile fractions, it will change into a different compound that may develop properties that could cause trouble later. It could get gummy, react with the glue, react with any water that leaks in, etc. The sealed interior space with multiple heating and cooling cycles is a pretty good little chemical reactor.

For a sealer he'd need something more stable and less volatile. If he really wants to use an oil, one of the more traditional furniture oils (tung oil, boiled linseed, etc.) might work better. Personally, I'd use epoxy, paint or varnish.

Good luck to him,



RE: sealing options other than epoxy

Some good technical info. The oil was my idea, he was thinking paint. Will pass this on to him. I have already sealed everything with epoxy so for my project the querie was purely academic Cheers

RE: sealing options other than epoxy

Does the board have any ports that can be opened for ventilation during storage? That might work better than anything to keep the wood healthy. A thorough paint job on the inside would probably be as good as epoxy, and certainly easier, and cheaper.



RE: sealing options other than epoxy

Hi Grant, It will require some way of venting. I expect that he will fit a screw or snap cap bung/ plug. I passed on Lazlo's info and oil is off the list. This is the board for anybody interested Reasonable plans and a site forum

RE: sealing options other than epoxy

For epoxy to work as a long term adhesive, the wood needs to be stable. To be stable, the wood must be kept dry. Nothing works as a better water (and moisture) barrier than epoxy. The Gougeons did lots of tests of this property- coating boards with various products and attaching them to dock pilings above and below the water, then checking the moisture content periodically over a year. Only epoxy kept the m/c stable, whether the sample was immersed or in the air, in dry and humid seasons.

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